1. Field of the Invention
The present invention relates to modulating digital communications and more particularly to a modulation system and scheme utilizing infrared energy that is compatible with the asynchronous IRDA standard format as well as a synchronous format for infrared (IR) communications.
2. Problem to be Solved
The Infra Red Data Access Standard (IRDA) committee has adopted as its modulation scheme the use of a Flash pulse of either a 3/16 bit cell width or of a fixed 1.63 microsecond length whenever the data to be transmitted is zero in an asynchronous data format (with one start bit, one stop bit, and no parity bit). The demodulator prolongs the received pulse to a full bit cell width and inverts it to produce the correct level.
The IRDA modulation scheme further converts serial data from flash pulses to Non-Return-to-Zero (NRZ) format. While this is acceptable for an asynchronous transmission mode in which the NRZ line must change state at the beginning of each character, it is unacceptable for a synchronous mode where the NRZ line may not change state, i.e., its DC level, for a prolonged period of time. If consecutive 1's or 0's are received, the digital phase lock loop used in the demodulator for synchronous communication may lose the lock on the data if it is supplied in NRZ format. Consequently, the standard encoding technique lacks certain versatility and an alternative encoding method is required which is backwards compatible with the IRDA modulation while supporting higher speed synchronous communication.
3. Objects
It is therefore an object of the present invention to provide a modulation scheme that can support both asynchronous and synchronous data communication.
It is further object of the present invention to provide a Flash IR modulation scheme that can support both the IRDA standard and synchronous data communication.
It is another object of the present invention to provide a Flash IR modulation system that can support both the IRDA standard and synchronous data communication and is of low cost and easily implemented.